Milling tool for emptying the femoral medullary space and hip prosthesis to be inserted in the space created

ABSTRACT

Milling tool for emptying the femoral medullary space, while creating a space for the shaft of a hip prosthesis, which comprises a flexible core and a plurality of conical, rotationally symmetrical milling segments, mounted in superimposed manner on the core and provided with a central through-bore, the milling segments being so connected to the core and/or the milling segments adjacent thereto, that a rotational force applied to the core and/or the upper segment is transferred to the individual milling segments, as well as a hip prosthesis with a conically directed shaft and a ball mounted on the proximal end of the shaft and which comprises a flexible core, a plurality of conical, rotationally symmetrically segments, mounted in superimposed manner on the core and provided with a central through-bore and a device for tensioning the core to bring a stiffening of the shaft formed from the individual segments.

CROSS-REFERENCES TO RELATED APPLICATIONS

This is a Divisional Application of patent application Ser. No.09/381,486 now U.S. Pat. No. 6,283,970 filed Sep. 20, 1999 of the sameinventor which was filed as PCT/DE 98/00763 filed Mar. 14, 1998.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OF DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to a milling tool for emptying the femoralmedullary space, whilst creating a space for the shaft or shank of a hipprosthesis and a hip prosthesis suitable for insertion in said space.

The insertion of a hip prosthesis comprising a shaft and a ball to beattached at an angle thereto is a frequent, regularly relativelyuncomplicated surgical operation.

However, difficulties arise in those cases in which the femoralmedullary space to be emptied with the aid of a milling tool prior tothe insertion of the hip prosthesis shaft is not straight, but insteadcurved, because then when using the conventional, straight milling toolsregularly and in undesired manner bony substance to be maintained isalso milled off.

2. Background Art

DE 29 14 455 discloses a device for producing a cavity in a bone for theinsertion of an artificial joint part, in which two rasp halves adaptedto the shape of the bone cavity to be produced are placed on a flexibleturning tool drive shaft, the two rasp halves being movable against oneanother in the axial direction.

WO 94/27507 discloses a milling tool for emptying the femoral medullaryspace, whilst creating a space for the shaft of a hip prosthesis, havinga flexible core and a plurality of conical, rotationally symmetricalmilling segments, mounted in superimposed manner on the core andprovided with central through-bores, which transfer or transmit arotational force applied to the core. The pins provided therein fortransferring the rotational force shear off, however, on bending thecore in non-straight femoral medullary spaces.

SUMMARY OF THE INVENTION

The problem of the invention is to provide a milling tool making itpossible to create a space for a hip prosthesis shaft following the pathof the femoral medullary space, as well as a hip prosthesis, which canbe inserted in such a non-straight, emptied femoral medullary space.

According to the invention this problem is solved by a milling tool foremptying the femoral medullary space, whilst creating a space for theshaft of a hip prosthesis, having a flexible core and a plurality ofconical, rotationally symmetrical milling segments, mounted insuperimposed manner on the core and provided with central through-bores,which transmit a rotational force applied to the core, and a device fortensioning the core. According to the invention the above-stated problemis also solved by having a hip prosthesis having a conically directedshaft and a ball mounted on the proximal end of the shaft, wherein thehip prosthesis comprises a flexible core, a plurality of conical,rotationally symmetrical segments, mounted in superimposed manner on thecore and provided with a central through-bore and a device fortensioning the core bringing about a stiffening of the shaft formed fromthe individual segments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail hereinafter relative to thedrawings, wherein:

FIG. 1 is diagrammatic representation of such a milling tool in anuntensioned core.

FIG. 2 is representation corresponding to FIG. 1 for a tensioned core.

FIG. 3 is hip prosthesis with an untensioned core.

FIG. 4 is representation corresponding to FIG. 3 for a tensioned core.

DETAILED DESCRIPTION OF THE INVENTION

The milling tool shown in FIGS. 1 and 2 comprises a flexible core and aplurality of conical, rotationally symmetrical milling segments providedwith a not shown, central through-bore and mounted in superimposedmanner on the core 10.

The core is cross-sectionally noncircular and the through-bore of themilling segments 12 is provided with a correspondingly noncircular,axially directed through-bore (additively or alternatively the end facesof the individual milling segments 12 pointing towards one another canalso be provided with meshing radial serrations). The central throughbores have wasp waist cross-sections.

The core is provided with a tensioning device 14 acting on the uppermilling segment 12 and whose tightening tensions the core 10 against theupper milling segment 12 and consequently beings about a mutualstiffening of the milling segments 12 (and consequently the shaft formedfrom the individual milling segments 12).

The drawing also shows that the end faces of the milling segmentspointing towards one another are slightly convex, so that they can rollon one another.

The lowermost milling segment 12 is firmly attached to the core 10.

For emptying the femoral medullary space the milling tool is attached inthe conventional manner with the core 10 untensioned. The distal millingsegment 12 (the tip firmly connected to the core 10) will follow thepath of the relatively soft femoral medullary space and the followingmilling segments follow this pate. During the rotation of the millingtool resulting from the application of a rotational force to the coreand/or the upper milling segment, they mainly only empty the softmaterial of the femoral medullary space, thereby protecting the bone.Thus, the milling tool “meanders” through the curved femoral medullaryspace and empties the same whilst protecting the bone material.

The hip prosthesis shown in FIGS. 3 and 4 has a correspondingconstruction. It comprises a flexible core 10, a plurality of conical,rotationally symmetrical segments, mounted in superimposed manner on thecore 10 and provided with a central through-bore and a device 14 fortensioning the core 10 bringing about the stiffening of the shaft formedfrom the individual segments 12.

In the state shown in FIG. 3 in which the core 10 is not tensioned, thehip prosthesis shaft is driven into the previously emptied (not strictlylinearly directed) femoral medullary space. During this process theindividual segments 12 are so oriented (i.e. tilt with respect to theimaginary shaft axis), that the shaft is adapted to the femoralmedullary space.

Following the driving in of the shaft core 10 is tensioned, so that theshaft is stiffened and loaded in the direction of an increasingstraightening, which, due to the elasticity of the bone material, leadsto a large-area engagement of the segments forming the shaft on theretained bony substance and consequently permits a much greater forcetransfer of the prosthesis shaft to the femur than would be possiblewhen using a straight shaft.

What is claimed is:
 1. Hip prosthesis having a conically directed shaftand a ball (16) mounted on the proximal end of the shaft, characterizedin that the hip prosthesis comprises a flexible core (10), a pluralityof conical, rotationally symmetrical segments (12), mounted insuperimposed manner on the core (10) and provided with a centralthrough-bore and a device (14) for tensioning the core (10) bringingabout a stiffening of the shaft formed from the individual segments(12).
 2. Hip prosthesis according to claim 1, characterized in that thecentral through-bore has a wasp waist cross-section.
 3. Hip prosthesisaccording to claim 1, characterized in that the distally positionedsegment (12) is firmly attached to the core (10).
 4. Hip prosthesisaccording to claim 1, characterized in that the end faces of thesegments (12) are slightly convex.